Azeotropic composition

ABSTRACT

It is not intended that the following abstract of the disclosure be construed as limiting the invention in any manner. The disclosure relates to binary azeotropic mixtures of tetrachlorodifluoroethane and methanol. It has also been discovered that n-butanol or isobutanol or sec-butanol will form azeotropes with these halogenated solvents. The disclosure also relates to ternary azeotropes of tetrachlorodifluoroethane and trichloroethylene with methanol. It has also been discovered that ethanol or isopropanol will also form ternary azeotropes with these two halogenated solvents. In a further embodiment ternary azeotropes are disclosed comprising tetrachlorodifluoroethane, trichloroethane and methanol. It has also been discovered that ethanol and isopropanol will also form ternary azeotropes with these two halogenated solvents.

United States Patent Schofield et al.

[ June 20, 1972 [54] AZEOTROPIC COMPOSITION [72] Inventors: J. AllanSchofield, lrvington; Roger A.

[52] U.S. Cl. ..252/171, 252/66, 252/DIG. 9 [51] Int. Cl. ..Cl 1d 7/50,C23g 5/02 [58] Field ofSearch ..252/171, 66-68,

[56] References Cited UNlTED STATES PATENTS 3,085,] 16 4/1963 Kvalnes..260/652.5

OTHER PUBLICATIONS Rose Cond. Chem. Dict. 1956) 5th Ed. Reinhold Publ.Co. p. 186

Primary ExaminerLeon D. Rosdol Assistant Examiner-W. Schulz AttorneyPaulA. Rose, Louis C. Smith, Jr., Francis M. Fazio and Robert J. Eichelburg[57] ABSTRACT It is not intended that the following abstract of thedisclosure be construed as limiting the invention in any manner.

The disclosure relates to binary azeotropic mixtures oftetrachlorodifluoroethane and methanol. It has also been discovered thatn-butanol or isobutanol or sec-butanol will form azeotropes with thesehalogenated solvents.

The disclosure also relates to ternary azeotropes oftetrachlorodifluoroethane and trichloroethylene with methanol. It hasalso been discovered that ethanol or isopropanol will also form ternaryazeotropes with these two halogenated solvents.

In a further embodiment ternary azeotropes are disclosed comprisingtetrachlorodifluoroethane, trichloroethane and methanol. It has alsobeen discovered that ethanol and isopropanol will also form ternaryazeotropes with these two halogenated solvents.

3 Claims, No Drawings AZEOTROPIC COMPOSITION This is a division ofapplication Ser. No. 677,715 filed Oct. 24, I967 now U.S. Pat. No.3,554,918.

This invention relates to an azeotropic composition and particularly tothe binary and ternary azeotropic mixture of tetrachlorodifluoroethaneand methanol or any one of the isomers, n-butanol or iso-butanol orsec.-butanol. The present invention also relates to ternary azeotropesof tetrachlorodifluoroethane and trichloroethylene with either methanolor ethanol or isopropanol. in a further embodiment ternary azeotropeshave been discovered comprising tetrachlorodifluoroethane,trichloroethane and either methanol or ethanol or isopropanol.

Several of the chlorofluoroethanes have attained widespread use asspecialty solvents in recent years, particularlytetrachlorodifluoroethane. This is a relatively high melting compound(CCl FCCl F, 24.5 C.), which is nontoxic and nonflammable, and which hassatisfactory solvent power for greases, oils, waxes and the like undercertain conditions. it has therefore found use in cleaning electricmotors, compressors, lithographic plates, typewriters, instruments,gauges, and as non-corrosive brines.

For certain solvent purposes however, the chlorofluoroethanes alone haveinsufficient solvent power. This is particularly true in the electronicindustry during the manufacture of printed circuits." Printed circuitsare well known in the electronics art; and consist of a circuit formedfrom a soft metal on a solid, non-conducting surface such as areinforced phenolic resin. During manufacture, the solid surface iscoated with the metal, the desired portion of metal is coated with animpervious coating, and the excess metal is removed by etching with asuitable acid. After the excess metal has been removed, it is necessaryto remove the impervious coating because solder joints must be made tothe printed circuit and these will not form if the coating is present.After the impervious coating is removed, the circuits are coated with arosin flux to permit the joints to be soldered, after which the rosinflux must then be removed.

The chlorofluoroethane solvent does not have sufficient solvent power toclean printed circuits;" that is, to effectively remove the rosin flux.Although mixtures of solvents may be used for this purpose they have thedisadvantage that they boil over a range of temperatures andconsequently undergo fractionation in vapor degreasing or ultrasonicapplications which are open to the atmosphere. When employing either ofthese cleaning or degreasing methods the solvent must also be bothrelatively nontoxic and nonflammable for safety reasons.

Tetrachlorodifluoroethane is a relatively high boiling fluorocarbon andfor this reason is especially advantageous in \apor degreasingapplications since at these temperatures the hot vapor has more of atendency to dissolve high melting greases. or fluxes as well as oilresidues and the like. When articles such as circuit boards are passedthrough a vapor degreaser, the solvent vapors tend to condense on thearticle until the articles are heated by the vapors from roomtemperature up to the temperature of the vapor. The condensation thusformed on the articles tends to drip back into the solvent reservoirtaking with it some of the soil on the article. For this reason theability of a cleaning solvent to condense on the surface is especiallyadvantageous. Higher boiling solvents prolong this condensation effectin a continuous degreaser since it takes a greater amount of time tobring the article passing through the degreaser up to the vaportemperature of the solvent. Consequently higher boiling solventsgenerally have better cleaning power per unit of time in a continuousvapor degreaser than the lower boiling solvents.

Tetrachlorodifluoroethane also is a better solvent than materials suchas trichlorotrifluoromethane, however, it suffers the disadvantage thatit is solidus at room temperature whereas the latter is liquidus.Accordingly tetrachlorodifluoroethane' is more difficult to handle thanliquid type cleaning solvents.

It is an object of this invention to provide a constant boiling orazeotropic solvent that is a liquid at room temperature, will notfractionate and also has the foregoing advantages. Another object is toprovide an azeotropic composition which is valuable as a solvent andparticularly for cleaning printed circuits. A further object is toprovide an azeotropic composition which is both relatively nontoxic andnonflammable both in the liquid phase and in the vapor phase and whichat the same time is an excellent solvent for cleaning printed circuitsespecially by means of a continuous vapor degreasing machine.

The above object of this invention may be accomplished by a novel binaryazeotropic composition of tetrachlorodifluoroethane (e.g.,l,l,2,2-tetrachlorol ,2- difluoroethane) and either methanol orn-butanol or secondary butanol or iso-butanol; ternary azeotropes oftetrachlorodifluoroethane (e.g., l,l ,2,2-tetrachloro- 1,2-difluoroethane) trichloroethylene and either methanol or ethanol orisopropanol; and ternary azeotropes of tetrachlorodifluoroethane e.g. l,l ,2,2-tetrachloro-l ,2-difluoroethane), trichloroethane (e.g.,l,l,l-trichloroethane) and either methanol or ethanol or isopropanol.Although l,l,2,2-tetrachloro l,2-difluoroethane is a preferredtetrachlorodifluoroethane, the isomer 1 l l ,2-tetrachloro-2,2-difluoroethane may be substituted therefore in whole or in part andespecially in minor amounts or trace amounts. The preferredtrichloroethane comprises the l,l,l-trichloroethane isomer. All of thesemixtures form azeotropes which distill at a constant temperature, theliquid phase and the vapor phase in equilibrium therewith having thesame composition. Such mixture is relatively nonflammable and nontoxicin both the liquid phase and the vapor phase. These mixtures areparticularly useful as solvents for greases, oils, waxes, and the likeand cleaning electric motors, compressors, lithographic plates,typewriters, precision instruments, gauges, and the like and areparticularly useful for cleaning printed circuits.

Although the azeotropic mixtures are obtained at approximately 760 mm Hga variation in pressure and consequently a change in the compositionsand boiling points are also intended to be within the broad scope of theinvention. Thus the azeotropes may contain many different proportions ofall of the aforementioned components provided a constant boiling mixtureis obtained at the various pressures at which the compositions are used.Stated otherwise any pressure may be employed to obtain the azeotropesof this invention as long as a three component or two component constantboiling mixture is obtained, and accordingly the ratio of components ofthe azeotropes of the invention will also vary. The variation ofcomponents is thus within the skill of the art and is easily determinedonce it is known that the halogenated hydrocarbons of this inventionwill form the aforementioned azeotropes. In a preferred embodiment thepresent invention relates to the aforementioned azeotropes that boil atatmospheric pressureiabout 25, especiallyiabout l5 mm Hg.

EXAMPLE I Components Composition Percent Boiling Point, by Weight F, 760mm Hg 1, l ,2,2-tetrachloroethane 69.3

methanol 30.7

EXAMPLES lI-X The method of example I is repeated using differentmixtures of alcohols and/or l,l,l-trichloroethane or trichloroethyleneand l ,1 ,2,2-tetrachloro-l ,2-difluoroethane, the results of which areas follows:

COMPONENTS, PERCENT BY WEIGHT Example N umber M ethanol Ethanoli-Propanol Printed circuit boards are usually prepared by impregnatingglass cloth. nylon, or paper laminates with a phenolformaldehyde resinor an epoxy resin. Printed circuits are prepared by a variety ofmethods. In a typical procedure, the board consists originally of aphenolic resin impregnated base to which is bonded a sheet of copper, 2to 4 mils thick, covering one surface of the board. The desired circuitis drawn on the copper with an asphalt based ink using the silk screenmethod. The excess copper is then removed by etching with a ferricchloride-hydrochloric acid bath, sometimes containing ammonium chloride,leaving on the board the copper that is covered by the ink. Afterwashing off the etch solution, the asphalt ink is removed by cleaningwith the azeotropic composition of this invention in an ultrasonic bath(some mechanical scrubbing is often used). The entire surface of theboard is coated with a rosin flux and dried. The electronic components(resistors, capacitors, etc.) are then added at the proper places forsoldering to the circuit. The board is then passed over a molten solderbath, contacting the desired joints -with the molten metal, whereby thesoldering is effected. After n-Butanol 1,1,1-t1'ichloroethane Boilingmm. Hg. pressure Trichloroi-Butanol s-Butanol ethylene 32 kilocycles persecond at about l0-20 F. below the boiling point of the particularazeotrope for about one minute.

When the board is cleaned with the azeotropic mixtures of this inventionsubstantially all of the rosin flux is removed without any detrimentaleffect on the board which constitutes the backing of the printedcircuit.

Although the invention has been described by reference to some preferredembodiments it is not intended that the broad scope of the novelazeotropic compositions be limited thereby but that certainmodifications are intended to be included within the spirit and broadscope of the following claims.

What is claimed is:

1. An azeotropic composition consisting essentially of about 65 parts,by weight, of 1,1,2,2-tetrachloro-l,Z-di-fluoroethane and about 35 partsisobutanol.

2. A method for cleaning a solid surface comprising contacting saidsurface with the composition of claim 1.

3. A method in accordance with claim 2 wherein said composition is invapor form.

2. A method for cleaning a solid surface comprising contacting saidsurface with the composition of claim
 1. 3. A method in accordance withclaim 2 wherein said composition is in vapor form.